Integrated circuits generally comprise a multiplicity of circuit parts, such as various components and electrical lines, for example, which are connected to one another in a manner predetermined by the respective application. During operation of the integrated circuit, a circuit part may frequently change between a plurality of operating states, which can be manifested by a specific electrical potential of the respective circuit part. When its operating state changes, the circuit part is then subjected to charge reversal from a first to a second electrical potential, that is to say that its present electrical potential is pulled to a higher or a lower voltage level. Since circuit parts represent a greater or lesser capacitive load depending on their construction and function within the integrated circuit, the charge reversal of a circuit part is always associated with a charge transport manifested by a charge-reversal current. Said charge-reversal current can be drawn from a voltage network that provides the desired electrical potential. The circuit part is then electrically conductively connected to the voltage network for charge reversal. The voltage network can be fed for example by a voltage source outside the electronic circuit. Generally, only a small number of discrete voltage levels are made available to the circuit part by such an external voltage supply of the integrated circuit. However, further voltage levels within the voltage range of the external voltage supply can be generated relatively easily. However, if voltage levels are required which lie above or below the voltage range made available by the external voltage supply, it is necessary to use special voltage converters, such as e.g. internal voltage charge pumps. While other DC-DC converters (e.g. step-up or boost converters) generate their voltages on the basis of a reference potential with the aid of inductances, voltage pumps generate the higher or lower electrical potential provided with the aid of capacitances. Since voltage pumps can also be arranged in multistage fashion, they are particularly well suited to raising or lowering the discrete voltage levels made available by the external voltage supply within an extended voltage range in accordance with the respective application. In contrast to an external voltage supply, however, the maximum output current of a voltage pump is greatly limited by the magnitude of the capacitances and the frequency. Therefore, voltage pumps are used primarily if large output currents are not required. Furthermore, this type of voltage conversion is associated with a higher energy expenditure, for which reason drawing the charge reversal current from a pumped voltage network puts an additional burden on the total current consumption of the integrated circuit, where the additional burden depends on the magnitude of the desired voltage value and the pump stages required for this desired voltage value and also the efficiency thereof. This holds true especially during the charge reversal of large capacitances. Particularly in “low” power applications, that is to say applications having a reduced current consumption, however, the total current consumption of an electronic circuit represents a critical variable.
A concrete embodiment of this problem can be observed inter alia in integrated memory circuits, such as e.g. in a dynamic random access memory (DRAM), in which word lines are pulled from a high active voltage to a low blocking voltage level below the negative supply voltage with the aid of special driver circuits for the purpose of addressing specific memory areas. In this case, the blocking voltage level has to be generated by means of special pump stages, which put a relatively great burden on the total current consumption of the integrated circuit.
In order to reduce the total current consumption, therefore, integrated circuits are often designed in such a way that primarily circuit parts which require a relatively large charge-reversal current on account of their capacitance are operated as far as possible within the voltage range made available by the external voltage supply. However, such restrictions are often also associated with effects, such as e.g. higher leakage currents, which can affect the functionality of the entire integrated circuit.